Unsubstituted 2,2':6',2"-terpyridine is known to be an effective ligand for various metals. Most metal complexes thereof have heretofore been widely studied not only in the field of ligand chemistry but also in the field of analytical chemistry as they display various colors.
Recently, it has been found that metal complexes of 2,2':6',2"-terpyridine act as a photo-catalyst and are useful as a medium for conversion of solar energy.
On the other hand, there is almost no disclosure regarding substituted 2,2':6',2"-terpyridines in the literature (see, for instance, Abramovitch, Pyridine and Its Derivatives (John Wiley & Sons, 1974); Synthesis, page 1 (1976); Otto Meth-Chon, Comprehensive Heterocyclic Chemistry (Pergamon Press, 1984)). Only the following compounds are known as substituted 2,2':6',2"-terpyridines.
(1) 4'-Methanesulfonyl-2,2':6',2"-terpyridine (J. American Chemical Society, Vol. 109, page 3961, 1987) PA1 (2) 4'-Amino-2,2':6',2"-terpyridine derivative and 4'-phenoxy-2,2':6',2"-terpyridine derivatives (U.S. Pat. Nos. 4,555,477 and 4,568,633). PA1 where M represents a metal ion; PA1 Lig1 represents a compound as represented by the aforesaid formula (I); PA1 Lig2 represents a ligand to the metal ion M, except Lig1; PA1 A represents a counter ion to M(Lig1).sub.x (Lig2).sub.y ; PA1 x represents an integer of 1 or 2; and PA1 y and z each represents an integer of from 0 to 6.
2,2':6',2"-terpyridine derivatives where the 4'-position is substituted by an unsubstituted alkoxy group or an alkoxy group substituted by an aryl group, a heterocyclic group bonded via the carbon atom, an alkoxy group, an aryloxy group, an alkylthio group or an arylthio group are quite unknown up to the present.
On the other hand, development of dyes having a high wet heat-fastness is desired in the field of dyes.